How it works
The at command is often used to start a process at a later time. It can run any script at a specified date and time.
For instance, if you want the computer to send you a signal in one hour, use something like:
cat signal | at -q z now + 60 minutes
Assuming that the file named signal contains the commands necessary to generate the signal. Then in 60 minutes, the script will be execute and the signal will be heard or shown.